Removal of carbonyl sulfide from liquefied petroleum gas



April 29, 1952 REMOVAL OF CARBONYL SULFIDE FROM LIQUEFIED PETROLEUM GAS A. B. JOHNSON ETAL Filed April 23. 1949 INVENTORS Arfh L/f B../0hnson Dan/e/ H. Cond/f Patented Apr. 29, 1952 UNITED STATES PATENT OFFICE REMOVAL OF CARBONYL SULFIDE FROM LIQUEFIED PETROLEUM GAS Arthur B. Johnson, Orinda, and Daniel H. Condit,

Lafayette, Calif., assignors to California Research Corporation, San Francisco, Calif., a

corporation of Delaware Application April 23, 1949, Serial No. 89,286

in-part of our abandoned application Serial No.

764,438, filed July 29, 1947, for Removal of Carbonyl Sulfide from Liquefied Petroleum Gas.

Large quantities of liquefied petroleum gas are sold for use as household and automotive fuels. The basic materials for liquefied petroleum gas are C: and C4 hydrocarbons produced in the various refining and cracking processes to which crude oil is subjected. As obtained from these sources, the petroleum gases contain appreciable quantities of sulfur compounds which must be removed in order to produce a liquefied petroleum gas of commercially acceptable quality. Among the sulfur compounds commonly found in'petroleum gases is carbonyl sulfide. This compound is relatively unreactive, is present in very small amounts and is not effectively removed from the hydrocarbon gases by the conventional methods employed in removing hydrogen sulfide, mercaptans and the like. The usual object of the various desulfurization treatments applied to petroleum products by the industry is to reduce the sulfur content of the finished product below the point at which serious corrosion would be observed. In the case of liquefied petroleum gas, the maximum allowable sulfur content is ordinarily much lower than in other petroleum products. Even a very low sulfur content in liquefied petroleum gases is found to cause the formation of sulfur or sulfide deposits which cause faulty operation of the equipment in which the gas is used. Such troublesome deposits are most commonly formed in the orifices of gas-air mixing equipment in industrial gas systems and in carbureting units of automotive equipment. Slow accumulation of such deposits resulting in operational failure may occur even where the sulfur content of the gas is very low, consequently, highly efficient desulfurization is sought in the production of commercial liquefied petroleum gas.

Carbonyl sulfide has the general character of an acid anhydride. However, its corresponding acid, monothiocarbonic acid, is not known in the free state and reaction of carbonyl sulfide with water results in the slow formation of hydrogen sulfide and carbon dioxide. If a liquid petroleum gas containing carbonyl sulfide in addition to other sulfur compounds be subjected to a conventional desulfurization treatment, the treated gas, if tested shortly after treatment, shows no indication of the presence of corrosive sulfur; however, upon several days standing the gas responds positively to tests for corrosive sulfur compounds. The relatively unreactive characits hydrolysis to the more reactive hydrogen sulfide make efficient carbonyl sulfide removal by conventional desulfurization methods impossible.

Carbonyl sulfide does not appear to occur in virgin petroleum fractions but is formed in thermal and catalytic cracking processes. The amount of carbonyl sulfide so formed is uniformly small and its content in the liquefied petroleum gas fraction of cracked stocks will usually be on the order of several hundred parts per million.

Production of commercially acceptable liquefied petroleum gas from cracket petroleum requires efficient removal of carbonyl sulfide and its relatively unreactive character in combination with low content have made such removal a difficult and long standing problem.

Numerous methods and reagents have been proposed for this purpose, usually involving contact of the carbonyl sulfide containing hydrocarbons with a generally alkaline reagent. Various primary amines have been employed with varying degrees of success and strongly alkaline solutions or suspensions of weakly basic or amphoteric metallic hydroxides, the metals of which form insoluble sulfides, have been proposed. However, the employment of these carbonyl sulfide-reactive alkaline reagents in the contacting operations heretofore proposed has been characterized by prolonged contact time and incomplete carbonyl sulfide removal. According to one of these prior proposals, petroleum gases are passed, in gaseous phase, upwardly through a downwardly flowing stream of monoethanolamine in countercurrent flow to bring about a desired reaction between the carbonyl sulfide and monoethanolamine. According to another proposal, treatment of the contaminated petroleum gases in the liquid phase with monoethanolamine is contemplated and a solid adsorbent is proposed as a support for and extender of the monoethanolamine to bring the desired intimacy of contact and interreaction between the carbonyl sulfide and monoethanolamine.

It is the object of the present invention to provide a process for the removal of carbonyl sulfide from liquefied petroleum gas characterized by increased rapidity, efficiency, and economy. It is a further object to provide a method for more eifective employment of previously known carbonyl sulfide-reactive reagents.

It is another object to provide a new carbonyl sulfide-reactive alkaline reagent which is particularly effective in removing carbonyl sulfide from non-acidic gases containing carbonyl sulfide.

Pursuant to the present invention, normally gaseous petroleum hydrocarbons containing carbonyl sulfide are passed in liquid phase into a dispersing zone and there contacted with a liquid carbonyl sulfide-reactive treating agent. The liquefied hydrocarbon is dispersed in the treating agent forming an unstable emulsion which is passed into a settling zone where the emulsion rapidly breaks, forming an upper layer consisting of substantially pure liquefied hydrocarbons and a lower layer comprised of a major amount of treating agent containing reacted carbonyl sulfide and a minor amount of liquefied hydrocarbon dispersed in the treating agent. The upper hydrocarbon layer is continuously withdrawn as the finished product and the lower treating agent layer is continuously withdrawn and recirculated to the dispersing zone. The volume of treating agent recirculated to the dispersing zone substantially exceeds that of the fresh liquefied hydrocarbon feed charged thereto.

The appended drawing is a diagrammatic illustration of one arrangement of apparatus and process flow suitable for the practice of the invention.

To start the process, treating agent is introduced into settling tank 1 until this vessel is approximately half full. This may be done by any convenient method, for example, treating agent may be passed into tank I through lines 2, 9, and 8. When tank I is approximately half filled with treating agent, valve 20 is closed and centrifugal pump 4 is started, drawing treating agent from tank I through lines 8, 9, and 3 into the pump 4.

Simultaneously liquefied hydrocarbon gases containing carbonyl sulfide are permitted to flow 1 ing agent forming an unstable emulsion which is forced by pump 4 through lines 5, 6, and [4 into settling tank 1. Line M extends downward into tank I so that its open discharge end is approximately at the level of the surface of the treating agent layer. In tank I the unstable emulsion breaks rapidly, forming an upper layer of substantially pure hydrocarbons and a lower layer of treating agent containing reacted carbonyl sulfide and a minor amount of emulsified hydrocarbon, while there is some turbulence at the discharge end of line l4 preventing theestablishment of a static interface between the upper hydrocarbon layer and the lower treating agent layer the general interfacial area is indicated at level 23. The amount of emulsified hydrocarbon is minor in comparison to the volume of treating agent in which it is dispersed. However, in a preferred mode of operation the ratio of emulsified hydrocarbon in the treating agent layer to the treating agent in said layer may closely approach the ratio of fresh hydrocarbon feed to treating agent entering pump 4.

As operation as above described is continued, the separated hydrocarbon layer in tank 'I increases in depth until it finally fills the tank, and

flows through line [0. taken directly from line H] as a product but in preferred operation it passes through line [0 into a second settling tank ll. Line [0 extends into tank H and discharges hydrocarbons at a point about of the distance from the bottom to the top-of the tank. During continued operation, tank I! is filled with hydrocarbon which overflows through line 15 and which is recovered from line l5 as the finished product. The very small amount of treating agent carried into tank H forms a separate layer at the bottom of the tank, its interface with the hydrocarbon liquid being indicated at 24. Valve 2| may be opened from time to time and the treating agent layer which has accumulated in the bottom of tank I [drawn off and recirculated via lines 9 and 3 to pump 4.

The hydrocarbon may be Operation may be continued until the treating agent is spent at which time introduction of feed and circulation of treating agent may be stopped and the treating agent discharged from the system via lines 9 and 22. Fresh treating agent may then be charged to tank I and operation is resumed. However, spent treating agent may be periodically withdrawn through lines 9 and 22 and fresh treating agent may be periodically or continuously added to replace the reagent withdrawn or mechanically lost during the process. Continuous runs of several months duration can be made in this manner.

The above described embodiment of the process of the invention consists essentially of a closed circuit containing a dispersing zone constituted by a high speed centrifugal pump or turbo mixer adapted to produce an unstable emulsion of the liquefied hydrocarbon in the treating agent and a settling zone constituted by one or more tanks with the treating agent in continuous circulation and with the hydrocarbon feed entering the circuit at the dispersing zone, circulating for a period and leaving the circuit as it separates in the settling zone.

The following examples illustrate the removal of carbonyl sulfide from liquefied petroleum gases by the process of the invention.

In each of the examples the carbonyl sulfide content of the treated product was below about 0.04 part per million calculated as sulfur. The carbonyl sulfide contents in each case were determined by an arbitrary test which grew out of practical experience. In this test the treated gas is stored for 21 days to permit the slow hydrolysis of any carbonyl sulfide present to occur. The gas is then passed over silvered glass beads at 275-300" F. at a rate not exceeding 20-30 pounds per hour and any observed darkening of the beads is compared with a standard. If 20 pounds of the gas pass over the bead and do not cause a tarnish exceeding that of the standard beads the gas is considered satisfactory for all commercial uses and is known to contain les than about 0.04 part per million of carbonyl sulfide calculated as sulfur. The general procedure of this test has been described by M. M. Holm in Industrial and Engineering Chemistry, Analytical edition, July 15, 1936 at pages 299-300.

An alternative test which may be employed and which was employed in checking the carbonyl sulfide content and degree of removal in Example V below is a determination of hydrogen sulfide and free sulfur in a sample of gas which has been stored for 21 days to permit decomposition of corbonyl sulfide. Hydrogen sulfide is determined by color test with alkaline lead acetate and free sulfur is determined by color test with Dr. Simons Reagent supplied for this purpose by Capitol Chemical Company of Washington, D. C. This test has been coordinated with the silver bead test for accuracy.

EXAMPLE I The treating agent here used is a particularly effective carbonyl sulfide-reactive alkaline reagent consisting of a mixture of 20% by weight monoethanolamine in aqueous solution and 10 Be. aqueous caustic soda, 33.2 volume per cent of the mixture being monoethanolamine solution and the remainder being caustic soda solution. Thus, both reagents are present in a concentration of about 1.2 mols/liter. The liquified petroleum gas from thermally cracked petroleum treated consisted principally of propane and propylene and was given conventional pretreatments to remove hydrogen sulfide. The pretreated liquefied petroleum gas contained 700 parts per million by weight of carbonyl sulfide calculated as free sulfur. It was subjected to the action of the treating agent in a treating system conforming essentially to that shownin the appended drawing. The temperature in the system was maintained at 100 F. and the pressure at 250-270 p. s. i. sufiicient to maintain the petroleum gas in liquid phase. The volume ratio of treating agent to fresh feed entering the mixing zone was 31 to 1. The hydrocarbon liquid effluent from the settling zone was distilled to remove any free sulfur which may have been formed during the treatment. Analysis of the treated product showed a carbonyl sulfide content of less than 0.04 part per million calculated as free sulfur.

EXAMPLE II The treatment of Example I was performed on liquefied petroleum gas recovered from the product stream of a catalytic cracking operation. This gas following pretreatment to remove hydrogen sulfide and mercaptans was found to contain 100 parts per million by weight of carbonyl sulfide calculated as free sulfur. Following treatment by the process of the invention, the hydrocarbon gas product contained less than 0.04 part per million of carbonyl sulfide calculated as free sulfur.

EXAMPLE III A carbonyl sulfide reactive alkaline reagent was prepared by mixing equal volumes of 33% caustic potash and ethyl alcohol. Liquefied petroleum gas forni'ed in the thermal cracking of petroleum and containing 700 parts per million of carbonyl sulfide calculated as free sulfur was dispersed in the alcoholic caustic potash treating agent in a dispersion zone to form an unstable emulsion. The volume ratio of treating agent to liquefied gas in the dispersion zone was 2 3 to 1 and the volume ratio of liquefied petroleum gas treated per hour to the total volume of treating agent in the system was 4.3 to 1. The unstable emulsion was passed from the dispersion zone to a settling zone where it rapidly broke, forming a supernatant layer of treated liquefied petroleum gas which was withdrawn and analyzed and a layer of treating agent which was recirculated to the dispersion zone. The treated liquefied petroleum gas contained less than 0.04 part per million of carbonyl sulfide calculated as free sulfur. During this run a substantial quantity of alcohol was lost.

EXAMPLE IV The liquefied petroleum gas of Example 111 was treated with a carbonyl sulfide reactive alkaline reagent made up by mixing equal volumes of aqueous cresylic acid containing 7.1 mols of acid per gallon and sodium hydroxide containing 11.4 mols of sodium hydroxide per gallon and adding water in amount equal to the volume of the mixture. The volume ratio of treating agent to liquefled petroleum gas in the dispersion zone was 85 to 1 and the ratio of liquefied petroleum gas treated per hour to total treating agent employed was 1.4 to 1. The treated liquefied petroleum gas contained less than 0.04 part per million of carbonyl sulfide calculated as free sulfur.

EXAMPLE V A commercial scale run of two weeks duration was made. The apparatus conformed generally to that illustrated in Figure 1. Settling tank 23 was charged with 23 barrels of reagent having the following composition by weight: monocthanolamine, 5.8%; sodium hydroxide, 14.0%; water, 80.2%. A hydrocarbon feed consisting principally of propane from thermal and catalytic cracking units was pretreated to remove hydrogen sulfide and mercaptans and then treated with the monoethanolamine-caustic reagent to remove carbonyl sulfide and residual hydrogen sulfide. The feed was put through the treating unit at an average rate of 500 barrels per day. The monoethanolamine-caustic reagent was circulated by pump 4 at a rate of 13,000-16,000 barrels per day. The monoethanolamine-caustic reagent as removed from settling tank 23 for recirculation had a suspended hydrocarbon content of 20-25 per cent and the circulated volumes indicated above include this hydrocarbon material. The following Table I summarizes the results 0 this run.

TABLE I Consumption rates for test run on MEA treater Av Rate Total Av. Rate Av. Cone. Total Lb. Total Lb. Total Lh. No. of of LPG EEL E LS of COS Moles of a g g Moles of Moles of Hours Throughut 5 Removed, cos Re NaOH Mm Run 1 put, BPD p p. p. m. moved 1 Consumed 1 Consumed l Lb./day

l (O. 19) (2. 97) 236.25. 661 4, 917. 3 206 6. 63 247. 0 24. 73 l. 42

1 Totals here are for the over-all time elapsed betwee the start of the test run and the time of making the observations recorded in the horizontal rows of data.

Figures in parentheses in each case refer to consumptions occurring in the time interval between successive horizontal rows of data.

Of the several carbonyl-sulfide-reactive treating agents employed, the monoethanolaminecaustic reagent of Examples I, II and V is preferred on the basis of over-all efliciency and economy. It will be noted from Table I that monoethanolamine is not consumed in the reaction and that the mol ratio of caustic consumed to carbonyl sulfide removed is approximately 4 to 1. Since the treating reagent contains substantial proportions of sodium carbonate, sodium sulfide, sodium bicarbonate and sodium bisulfide in the latter stages of the run, analysis becomes difficult and it is believed that the mol ratio of 4 to 1 for caustic consumed to carbonyl sulfide removed represents the actual proportions in which these materials react. The small loss of monoethanolamine indicated at the end of the run is only an apparent loss, resulting from a change in concentration of monoethanolamine in the treating agent caused by dilution of the treating agent with caustic carried over from the pretreater and moisture picked up from the feed. The finding that monoethanolamine is not consumed in the reaction is unexpected, since monoethanolamine in the absence of caustic has been reported to react with carbonyl sulfide. In the presence of a strongly alkaline reagent, such as caustic, it appears to function either as a solubilizer or as a catalyst, facilitating the reaction of carbonyl sulfide with the strongly alkaline reagent.

is especially preferred, reagents consisting of monoethanolamine and other strongly alkaline materials, such as alkali metal hydroxides other than sodium hydroxides and alkali metal salts of weak acids, such as sodium carbonate, may be employed. In general, any alkaline material having a pH value above about 10 in 0.1 N solution may be mixed with monoethanolamine to give a solution which is operative. agents of higher pH values and high solubility have the marked practical advantage of longer process life.

In the run of Example V, carbonyl sulfide was substantially completely removed from the feed until the final hours of the run when the concentration of available alkalinity as sodium hydroxide in the treating reagent had fallen below 3% by weight. Available sodium hydroxide was determined by titration to phenolphthalein end r point, which not only neutralized sodium hydroxide present as such, but also converted sodium sulfide and sodium carbonate present in the reagent to sodium bisulfide and sodium bicarbonate, respectively. When this caustic concentration was reached, the monoethanolamine concentration was 5.3% by weight, having been reduced to this value from the initial 5.8% by dilution of the reagent. The solution with this high monoethanolamine concentration was ineffective at an available caustic concentration below 3%.

Other runs were made to determine the effect of varying monoethanolamine concentration in the treating reagent. It was found that the monoethanolamine concentration must be maintained above 1.5% by weight in order to obtain effective carbonyl sulfide removal. Accordingly, the treating reagent to be effective must have a titratable alkalinity greater than that of 3% sodium hydroxide and a monoethanolamine concentration above 1.5% by weight. In the practice of the invention a reagent having a monoethanolamine concentration above about 3% and sodium hydroxide concentration above 10% by weight is ordinarily employed and a reagent con- However, re- H taining 4-6% monoethanolamine and sufiicient caustic to give a mol ratio of caustic to monoethanolamine of 3 to 6. is preferred. The reagent employed in Example V is illustrative of the preferred reagent.

During an extended run the caustic content of the solution is expended and when the titratable alkalinity falls to about 3 2 to 3 barrels of fairly concentrated caustic solution, for example 25 B. caustic, are added to the treating agent and the run continues. When the titratable acidity is again reduced to about 3% further addition of caustic is made. The capacity of settling tank I is ordinarily somewhat more than twice the volume of treating agent employed so that a considerable volume of caustic may be added. In practice it is found that mechanical losses of treating agent tend to offset the volume increases due to the caustic additions, and that after an extended run the caustic additions, solution losses and carry-over of pretreating solution combine to reduce the monoethanolamine concentration to below about 1.5%. When this occurs approximately one-half of the volume of treating agent in the system is dumped and replaced by fresh reagent. This is done without interrupting the introduction of feed into the treating system. By operating in this manner continuous runs of long duration may be made, their length being limited only by stoppages for repair or inspection of the While the monoethanolamine-caustic reagent equipment.

It is a characteristic of the process of the invention to maintain high ratios of treating agent to feed in the dispersion zone. In Example I this ratio was 31 to 1, in Example III it was 28 to 1, in Example IV it was 85 to 1, and in Example V it varied from about 13 to 1 to about 36 to 1. It has been found that in large-scale commercial mixing equipment currently available, the ratio must be maintained above about 10 to 1 in order to obtain a satisfactory removal of carbonyl sulfide from the feed.

The hydrocarbons which constitute the usual feed to the process of the invention ordinarily have a carbonyl sulfide content in the range 200-1200 parts per million and may contain in addition minor amounts of hydrogen sulfide which pretreatment with caustic fails to remove. Both of these gases are substantially completely removed by the treating reagents disclosed above.

The process is ordinarily conducted at temperatures of 70 to 120 F. and under a pressure in the range 250-300 p. s. i. sufficient to maintain the hydrocarbon in liquid phase. The space velocities employed in the process are high; usually the volume of liquid hydrocarbon treated per hour substantially exceeds the total volume of treating agent in the system and successful removal of carbonyl sulfide has been readily obtained when the volume of liquid hydrocarbon treated per hour was 4 times the total volume of treating agent in the system.

The feature of intimately dispersing the liquefied hydrocarbons in an excess of treating agent appears to contribute importantly to the eflicient carbonyl sulfide removal obtained at high feed rates. The stocks treated in the experiments summarized in Table I were also treated using the treating agents of the examples disposed in a conventional packed column through which the liquefied hydrocarbons were passed upwardly. In no case was satisfactory carbonyl sulfide removal obtained. Even when a space rate of one volume of hydrocarbons per volume of treating agent per hour was used the product was found only slightly improved when tested by the above described silver bead'test. The necessary intimate dispersion of the liquefied hydrocarb'onsto form an unstable emulsion may be obtained by the use of 'a centrifugal pump as described in reference to the appended drawing or by the use of an efli-cient turbomixer.

In the carbonyl sulfide separations illustrated in Examplesl and II and in Table I, the dispersing means found suitable in producing the desired unstable emulsion of liquefied petroleum gas in the treating agent was acentrifugal pump having a capacity of 300 gal./hr. and operating at 1750 R. P. M. Two and one-half gallons of treating agent were charged to the system for each run. In Run 3 of Table I, 9.5 gallons of liquefied petroleum gas were treated during each hour, which meant that 290.5 gallons of treating agent passed through the pump each hour so that 2.5- gallons of treating agent in the system were circulated through the pump about 116 times each hour. Operation in this manner produced the eificient carbonyl sulfide removal above described.

The dispersing power of this ump and the persistence of the unstable emulsion produced by it were studied by continuously circulating 2.5 gallons of a mixture consisting of 65% of 20 Be. caustic soda and 35% petroleum ether through it for varying periods of time. The following Table II shows circulation times; used and the cor-- responding times required for complete separation of the liquids on standing.

Tl ism II Any dispersing means which produces an unstable emulsion showing a comparable relation between circulation and settling times with this caustic-petroleum ether mixture may be satisfactorily employed in the process of the invention.

Since free sulfur may be formed prior to the contact of the liquefied petroleum gas with the carbonyl sulfide-reactive alkaline treating agents, the liquefied gas effluent from the settling zone is ordinarily distilled to remove any free sulfur which may have formed. If it is desired to avoid this distillation step, the composition of the treating agent may be modified by including sodium polysulfide as a constituent in amount sufiicient to give it a sodium polysulfide concentration of about 0.01% by weight.

While the process of the invention is especially Well adapted to the removal of carbonyl sulfide from normally gaseous hydrocarbons, it may be employed to remove carbonyl sulfide from other gaseous mixtures which contain carbonyl sulfide. For example, the synthesis gas charged to a Fischer-Tropsch synthesis or to an OX reaction as prepared from the usual materials such as coal or natural gas, frequently contains minor proportions of carbonyl sulfide which adversely affect the catalysts employed. Carbonyl sulfide is readily removed from such gases by the monoethanolamine-caustic treating reagent of this invention and the removal maybe effected by gasfrom petroleum hydrocarbon gases containing carbonyl sulfide and substantially free of other sulfur-containing compounds, which comprises intimately dispersing said hydrocarbon gases in liquid phase in an aqueous solution of monoethanolarnine and an alkali metal hydroxide present in the solution in the proportions of 3-6 mols of alkali metal hydroxide per mol of monoethanolamine.

2. The method as defined in claim 1 wherein the alkali metal hydroxide is sodium hydroxide.

3. The method as defined in claim 1 wherein the alkali metal hydroxide is potassium hydrox ide.

4. The method of removing carbonyl sulfide from carbonyl sulfide-containing normally gaseous hydrocarbons which comprises passing said hydrocarbons in liquid phase into a substantially greater volume of a treating agent comprised of monoethanolamine and an alkali metal hydroxide in aqueous solution into dispersing zone'an'd there dispersing the hydrocarbon liquid in said treating agent forming an unstable emulsion, passing said emulsion to a settling zone and there separating an upper layer comprised of substan tially pur liquefied hydrocarbons and a lower layer comprised of a major amount of said treat= ing agent containing reacted carbonyl sulfide and a minor amount of liquefied hydrocarbon dispersed in said treating agent, continuously with= drawing said upper hydrocarbon layer as the finished product and continuously withdrawing said lower layer, recirculating it to the dispersing zone and maintaining in the dispersion zone a volume ratio of treating agent to hydrocarbon of at least 10: 1.

5. The method of removing carbonyl sulfide from carbonyl sulfide-containing normally gaseous hydrocarbons which comprises continuously circulating a treating agent comprised of monoethanolamine and an alkali metal hydroxide in aqueous solution in a closed circuit con taining a dispersing zone and a settling zone, introducing said hydrocarbons in liquid phase into said dispersing zone in volume substantially less than the volume of treating agent circulating therethrough and there dispersing the liquefied hydrocarbons in treating agent forming an unstable emulsion of said hydrocarbons in said treating agent, separating the emulsion in said settling zone into an upper layer consisting of substantially pure liquefied hydrocarbons and a lower layer comprised of a major proportion of treating agent containing reacted carbonyl sulfide and a minor proportion of dispersed liquefied hydrocarbon, continuously withdrawing said upper layer as a product and continuously recirculating said lower layer to the dispersing zone while maintaining in the dispersion zone a volume ratio of treating agent to hydrocarbon of at least 10:1.

6. A method of purifying propane contaminated with sulfur compounds including carbonyl sulfide which comprises treating the propane with caustic soda under conditions suitable to remove sulfur compounds other than carbonyl sulfide, circulating an aqueous mixture of monoeth-anolamine and caustic soda cyclically through a closed circuit maintained under superatniospheric pressure sufiicient to maintain the propane in the liquid phase-and including an emulsifying or dispersion zone and 'an emulsion breaking and separation zone, introducing the carbonyl sulfide contaminated propane together with said circulated mixture into-the-emulsifying zone, the mixture being introducedin proportions by weight at least several times greater than the propane while maintaining within theemulsifying zone a volume-ratio of circulated mixure to propane of at least 10:1, intimately dispersing the propane throughout said circulated mixture with consequent rreactionof the carbonyl sulfide, conducting the emulsion or dispersion thus produced to the emulsion breaking and separation zone of sufiicient capacity to permit residence of the dispersion fora time suflicient to break the dispersionand separation of .a supernatant liquid of propane substantially freeof carbonyl sulfide and a lower layer constituted by the circulated mixture.

7. A process for removing carbonyl sulfide from carbonyl sulfide-containing'normally gaseous petroleum hydrocarbons comprising propane and butanes substantially free of other sulfur-containing compounds, which comprises passing .said hydrocarbons in liquid phase together with at least 10 times their volumes of a treating ,agent comprised of an aqueous solution ofmonoethanolamine and odium hydroxide in approximately equimolar concentrations into .a dispersing zone and there dispersing the liquefied hydrocarbons in the treating agent to form :an unstable emulsion, passing the emulsion'to .a:sett1ing zone and there separating it into an upper layer *comprised of "liquefied hydrocarbons containing less than-0.04 part per million'by weight-of carbonyl sulfide-calculated as free sulfurand alowerlayer comprising a major amount of treating agent containingreactedcarbonyl sulfide and a'minor lating the lower layer to the dispersing zoneyand maintaining a temperature of about 100 F. -'and a pressure of 250-270 p. s. i. .in the dispersing zone and in the settling zone.

8. 'The process as defined in claim 4 wherein the treating agent consists o'f 'an aqueous solution of monoethanolamine and sodium hydroxide'present in concentrations of 4-6% by weight :and 10-25% by weight, respectively.

ARTHUR B. JOHNSON. DANIEL H. CONDIT.

REEERENCES CITED The following references are of record in the file of this patent:

"UNITED STATES PATENTS Number Name Date 12,309,871 Schulze et al Feb. 2, 1943 2,311,342 Kerns et al Feb. 16, 1943 2,434,868 Sample et a1 Jan. 20, 1948 

1. THE METHOD OF REMOVING CARBONYL SULFIDE FROM PETROLEUM HYDROCARBON GASES CONTAINING CARBONYL SULFIDE AND SUBSTANTIALLY FREE OF OTHER SULFUR-CONTAINING COMPOUNDS, WHICH COMPRISES INTIMATELY DISPERSING SAID HYDROCARBON GASES IN LIQUID PHASE IN AN AQUEOUS SOLUTION OF MONOETHANOLAMINE AND AN ALKALI METAL HYDROXIDE PRESENT IN THE SOLUTION IN THE PROPORTIONS OF 3-6 MOLS OF ALKALI METAL HYDROXIDE PER MOL OF MONOETHANOLAMINE. 